Ejection control using substrate alignment features and print region alignment features

ABSTRACT

In a printing method, at least one image of a substrate supported in a printing system is acquired. An actual position of a first alignment feature on the substrate in a frame of reference of the printing system is determined based on the at least one image. Expected positions of second alignment features on the substrate are determined based on the actual position of the first alignment feature. Actual positions of the second alignment features in the frame of reference of the printing system are determined based on the at least one image and the expected positions of the second alignment features. Target positions of print regions on the substrate are determined based on the actual positions of the second alignment features. Ejection of print material onto the substrate in the print regions is controlled based on the target positions of the print regions.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Patent Application Ser. No.16/716,143, filed Dec. 16, 2019, and claims benefit of U.S. ProvisionalPatent Application Ser. Nos. 62/782,442, filed Dec. 20, 2018, and62/891,807 filed Aug. 26, 2019, each of which is incorporated byreference herein.

FIELD

Embodiments of the present application generally relate to inkjetprinting systems. Specifically, methods, systems and/or apparatuses forejection control in inkjet printing systems are described.

BACKGROUND

Inkjet printing is common, both in office and home printers and inindustrial scale printers used for fabricating displays, printing largescale written materials, adding material to manufactured articles suchas PCBs, and constructing biological articles such as tissues. Someprinting applications, such as printing light emitting materials on adisplay substrate, rely on extreme precision in positioning ofdispensing nozzles and/or print substrates. In some cases, error of morethan about 15 μm in placement of a droplet of print material can cause aprinting fault. Achieving such extreme precision is complicated bymyriad factors, such as manufacturing tolerances of printer components,thermal expansion, thermal non-uniformity, vibration, and evolution ofprinter component properties over time. Variation in substratepreparation can also introduce errors. In particular, prior to printinglight-emitting materials onto a display substrate, the locations for thelight-emitting materials are sometimes printed onto the substrate.Variation, or error, in printing the locations can lead to, andcompound, error in printing the light-emitting materials. Methods,systems and/or apparatuses for controlling ejection of print material inan inkjet printer are proposed in this aspect.

SUMMARY

In a printing method in accordance with one embodiment, at least oneimage of a substrate supported in a printing system is acquired. Anactual position of a first alignment feature on the substrate in a frameof reference of the printing system is determined based on the at leastone image. Expected positions of a plurality of second alignmentfeatures on the substrate are determined based on the actual position ofthe first alignment feature. Actual positions of the plurality of secondalignment features in the frame of reference of the printing system aredetermined based on the at least one image and the expected positions ofthe second alignment features. Target positions of a plurality of printregions on the substrate are determined based on the actual positions ofthe second alignment features. Ejection of print material onto thesubstrate in the plurality of print regions is controlled based on thetarget positions of the print regions.

In one embodiment, a printing system comprises a substrate supportconfigured to support a substrate, a printhead assembly havingdispensing nozzles, at least one imaging device, and a controller. Thecontroller is configured to control the at least one imaging device tocapture first images of a plurality of first alignment features on thesubstrate. The controller is further configured to determine actualpositions of the first alignment features in a frame of reference of theprinting system, based on the first images. The controller is furtherconfigured to determine expected positions of a plurality of secondalignment features based on the actual positions of the plurality offirst alignment features. The controller is further configured tocontrol relative positioning of the at least one imaging device and thesubstrate support based on the expected positions of the secondalignment features to enable imaging of the second alignment featuresusing the at least one imaging device. The controller is furtherconfigured to control the at least one imaging device to capture secondimages of the second alignment features. The controller is furtherconfigured to determine actual positions of the second alignmentfeatures in the frame of reference of the printing system, based on thesecond images. The controller is further configured to determine targetpositions of print regions corresponding to groups of the secondalignment features based on the actual positions of the second alignmentfeatures. The controller is further configured to control ejection ofprint material from the dispensing nozzles of the printhead assemblyonto the substrate in the print regions, based on the target positionsof the print regions.

In one embodiment, a controller for a printing system comprises at leastone processor. The processor is configured to receive image data of atleast one of a plurality of alignment features on a substrate supportedfor a print job in the printing system. The processor is furtherconfigured to determine actual positions of the plurality of alignmentfeatures in a frame of reference of the printing system, based on theimage data. The processor is further configured to determine targetpositions of pixels at corners of a print region on the substrate, basedon the actual positions of the plurality of alignment features. Theprocessor is further configured to determine target positions of pixelsalong edges of the print region, based on the target positions of thepixels at the corners of the print region. The processor is furtherconfigured to determine target positions of pixels in the print region,based on the target positions of the pixels along the edges of the printregion. The processor is further configured to control ejection of printmaterial from dispensing nozzles of a printhead assembly of the printingsystem onto the print region of the substrate, based on the targetpositions of the pixels in the print region.

In one embodiment, a flat panel display is made by a printing method inwhich at least one image of a substrate supported in a printing systemis acquired. An actual position of a first alignment feature on thesubstrate in a frame of reference of the printing system is determinedbased on the at least one image. Expected positions of a plurality ofsecond alignment features on the substrate are determined based on theactual position of the first alignment feature. Actual positions of theplurality of second alignment features in the frame of reference of theprinting system are determined based on the at least one image and theexpected positions of the second alignment features. Target positions ofa plurality of print regions on the substrate are determined based onthe actual positions of the second alignment features. Ejection of printmaterial onto the substrate in the plurality of print regions iscontrolled based on the target positions of the print regions.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a top isometric view of a printing system.

FIG. 2 is schematic top view of a printing system in accordance with oneembodiment.

FIG. 3A is a schematic side view of a printing system in accordance withone embodiment.

FIG. 3B is a schematic top view of a substrate in the printing system ofFIG. 3A in an example.

FIG. 4 is a flowchart of a printing method in accordance with oneembodiment.

FIGS. 5A-5D are schematic plan views of a substrate or a portion of asubstrate being processed at various operations of the printing methodin FIG. 4.

FIG. 6A is a flowchart of a printing method in accordance with oneembodiment.

FIG. 6B is a schematic plan view of a print region on a substrate beingprocessed in the printing method in FIG. 6A.

FIG. 7 is a flowchart of a printing method in accordance with oneembodiment.

FIG. 8 is a block diagram of a controller, in accordance with oneembodiment.

FIG. 9 is a schematic isometric view of a print assembly according toone embodiment.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components, values, operations, materials,arrangements, etc., are described below to simplify the presentdisclosure. These are, of course, merely examples and are not intendedto be limiting. Other components, values, operations, materials,arrangements, etc., are contemplated. For example, the presentdisclosure may repeat reference numerals and/or letters in the variousexamples. This repetition is for the purpose of simplicity and clarityand does not in itself dictate a relationship between the variousembodiments and/or configurations discussed. Further, spatially relativeterms, such as “beneath,” “below,” “lower,” “above,” “upper” and thelike, may be used herein for ease of description to describe one elementor feature's relationship to another element(s) or feature(s) asillustrated in the figures. The spatially relative terms are intended toencompass different orientations of the device in use or operation inaddition to the orientation depicted in the figures. The apparatus maybe otherwise oriented (rotated 90 degrees or at other orientations) andthe spatially relative descriptors used herein may likewise beinterpreted accordingly.

High precision in positioning of dispensing nozzles and/or printsubstrates is relied on in some inkjet printing applications to obtainprinted products of high quality. In order to precisely dispense printmaterial onto a substrate at very small target locations using an inkjetprinting system, it is useful to determine the actual positions of thesubstrate and/or print regions thereof in a frame of reference of theinkjet printing system. The actual positions of the print regions,defined in the frame of reference of the printing system, are then usedfor printing with high precision. The actual positions of the printregions are determined based on one or more print region alignmentfeatures on the substrate. Actual positions of the print regionalignment features are, in turn, determined based on one or moresubstrate alignment features. As a result, in at least one embodiment,the actual positions of all print regions on the substrate may bedetermined in a single frame of reference of the printing system, and asingle “firing” plan for a print job to print in all print regions onthe substrate may be developed while permitting for substratefabrication and/or printer measurement errors. Therefore, printing speedand accuracy are improved. This arrangement is advantageous over otherapproaches in which a limited set of marks are provided for determiningthe position of a substrate, without a separate set of marks fordetermining positions of individual print regions, and therefore,without the capability to correct for errors among the print regions onthe substrate.

FIG. 1 is a top isometric view of a printing system 100.

The printing system 100 has a substrate support 102, a print assembly104, and a holder assembly 106 for manipulating a substrate forprinting. The printing system 100 is founded upon a base 108, which isin one example a massive object to minimize vibratory transmissions tothe operative parts of the printing system 100. In one example, the base108 is a granite block. The substrate support 102 is located upon thebase 108, and comprises a support surface 110 along with a device formaking the support surface 110 substantially frictionless. In oneexample, the support surface 110 is an air table that provides a gascushion on which the substrate floats. The support surface 110 featuresa plurality of holes 112 that allow jets of gas to exit, thus providingan upward force to maintain a substrate at a desired elevation above thesupport surface 110. Some of the holes are configured to also allowcontrolled withdrawal of gas from the gas cushion floating the substrateto provide precise local control of substrate elevation.

The print assembly 104 comprises a dispenser assembly 114 disposed on aprint support 116. The print support 116 is disposed in relation to thesubstrate support 102 to provide access for the dispenser assembly 114to position constructively in relation to a substrate on the substratesupport 102 to precisely apply print material to the substrate. Theprint support 116 includes a rail or beam 117 that traverses thesubstrate support 102, allowing the dispenser assembly 114 to traversethe substrate support 102 and deposit print material at any location onthe substrate from one side of the print support 116 to the oppositeside thereof. In one example, the print support 116 is attached to thebase 108 and extends from the base 108 to provide stable support for thedispenser assembly 114. Two stands 120 extend from the base 108, onopposite sides of the substrate support 102, to the rail 117, whichextends across the substrate support 102. In one example, the stands 120and the rail 117 are both made of the same material as the base 108. Inone example, the stands 120, the rail 117, and the base 108 areintegrally formed from one piece of granite.

The dispenser assembly 114 includes at least one printhead assembly 119along with a print assembly controller 118 that includes electronicsand/or sensors for controlling the functional parameters of theprinthead assembly 119 such as location of the printhead assembly 119along the print support 116, timing, duration, type of print material,and dispensing profile. The printhead assembly 119 is movable along therail 117 of the print support 116 by operation of a print carriage 122that couples with the print support 116 to translate the printheadassembly 119 along the rail 117 from one end of the rail 117 to theother opposite end. In one example, the print carriage 122 is driven bya motor or a servomotor. Power and signal conduits are omitted tosimplify the figure.

A substrate (not shown in FIG. 1) is positioned under the print assembly104 by the holder assembly 106. The holder assembly 106 acquires securecontact with the substrate upon loading and moves the substrate alongthe substrate support 102 to position the substrate with respect to theprint assembly 104 for dispensing print material onto the substrate in aprecise fashion. The holder assembly 106 is located on one side of thesubstrate support 102 and extends along the substrate support 102 in afirst direction to translate the substrate in the first direction duringprinting. The first direction is denoted in FIG. 1 by arrow 124. Thefirst direction 124 is sometimes referred to as the “Y direction” or“scan direction.” The printhead assembly 119 moves in a second directionsubstantially transverse to the first direction, guided by the rail 117which extends substantially in the second direction denoted in FIG. 1 byarrow 126. The second direction 126 is sometimes referred to as the “Xdirection” or “cross-scan direction,” and the rail 117 as the “X beam.”A third direction substantially transverse to the first and seconddirections is denoted in FIG. 1 by arrow 125. The third direction 125 isreferred to as the “Z direction.” The X, Y and Z directions aredirections of axes of a coordinate system serving as a frame ofreference of the printing system 100, as illustrated by the arrows 124,125, and 126. In one example, the origin of the coordinate system is ata fixed point, e.g., associated with the base 108 or a home position ofthe dispenser assembly 114.

The holder assembly 106 is disposed on a holder assembly support 128,which in one example is a rail that extends in the first directionsubstantially the entire length of the substrate support 102 along anedge 130 of the substrate support 102. In one example, the holderassembly support 128 is attached to the base 108 to provide stablesupport for the holder assembly 106. In one example, the holder assemblysupport 128 is made from the same material as the base 108. In oneexample, the holder assembly support 128, base 108, and print support116 are integrally formed from one piece of granite. The holder assemblysupport 128 is referred to as a “Y beam.” The holder assembly 106 movesalong the holder assembly support 128 during operation to position thesecurely held substrate at any location on the substrate support 102,and the print assembly 104, for example by operation of the printassembly controller 118, positions the printhead assembly 119 to provideaccess to a precise location on the substrate for dispensing printmaterial.

A system controller 129 receives signals from various sensors deployedthroughout the printing system 100 and sends signals to variouscomponents of the printing system 100 to control printing. The systemcontroller 129 is operationally coupled, for example, via a network, tothe print assembly controller 118 and to a holder assembly controller131, which controls operation of the holder assembly 106. One or more ofthe substrate support 102, the print assembly 104, the holder assembly106, and other ancillary systems, such as environment control andmaterials management systems, have sensors operatively coupled to thesystem controller 129 to transmit signals to the system controller 129related to the status of various components during a printing operation.The system controller 129 includes data and instructions to determinecontrol signals to send to various controlled components of the printingsystem 100. In one embodiment, two or more of the system controller 129,the print assembly controller 118 and the holder assembly controller 131are integrated into a single controller. In one embodiment, at least oneof the system controller 129, the print assembly controller 118 and theholder assembly controller 131 is implemented as several controllersdistributed in the printing system 100 and connected one with anothervia a network. An example configuration of a controller in accordancewith one embodiment is described with respect to FIG. 7. For simplicity,in the description below, “controller” refers to any one or more ofcontrollers in the printing system 100.

To perform precision inkjet printing, microscopic droplets of printmaterial are placed in correspondingly small areas of the substrate. Forexample, in some cases print material droplets having diameter of 5-10μm are placed in an area of the substrate of dimension 10-15 μm. This isoften done while the substrate is moving in the Y direction (scandirection) to minimize print time. Such extreme precision is complicatedby many factors, such as tiny imperfections in the dimensions and/orpositions of the various parts of the printing system 100, variation ofthose dimensions with temperature, imprecision in the substrate,imprecision in speed of translation of the substrate, the dispenserassembly 114, and the holder assembly 106, and imprecision in thedistance of the substrate from the printhead assembly 119. For example,if positions of the dispensing nozzles in the printhead assembly 119 inthe frame of reference of the printing system 100 are not preciselyknown or controlled, it is difficult to control print material dropletsfrom the dispensing nozzles in the printhead assembly 119 for the printmaterial droplets to arrive at the target locations when the substrateis in the proper position. In some aspects, nozzle mapping is performedto determine or control positions of the dispensing nozzles in the frameof reference of the printing system 100. In further aspects, features ofthe substrate are recognized and also mapped to the frame of referenceof the printing system 100 to compensate for any misalignment of thesubstrate.

FIG. 2 is schematic top view of a printing system 200 in accordance withone embodiment. In one embodiment, the printing system 200 includes oneor more features of the printing system 100 described herein.

The printing system 200 includes a substrate support configured tosupport a substrate in a manner similar to the substrate support 102 ofthe printing system 100. For simplicity, the substrate support is notillustrated in FIG. 2; instead, a substrate 208 supported on thesubstrate support is shown. The printing system 200 further includes theprinthead assembly 119 having dispensing nozzles 206. In reality, thedispensing nozzles 206 may not be visible in a top plan view like FIG.2, and a representation of dispensing nozzles is shown in FIG. 2 forillustrative purposes. The circles represented as the dispensing nozzles206 are shown on a top surface of the printhead assembly 119, when infact the dispensing nozzles 206 are physically located on a nozzlesurface (not visible) of the printhead assembly 119 opposite the topsurface visible in FIG. 2. Thus, the circles representing the dispensingnozzles 206 show the positions of dispensing nozzles 206 on the nozzlesurface opposite the visible top surface. The printing system 200 alsoincludes the controller 118 and at least one imaging device coupled tothe controller 118.

In the example configuration in FIG. 2, the printing system 200 includestwo imaging devices, i.e., a first imaging device 201 and a secondimaging device 202. In an example, each of the first imaging device 201and second imaging device 202 includes a camera having an array of imagesensors arranged in multiple columns and rows to capture image data.Examples of image sensors include, but are not limited to, CMOS(complementary metal oxide semiconductor) and CCD (charge coupleddevice) sensors. The first imaging device 201 has a first, lowerresolution and a wider field of view 268. The second imaging device 202has a second, higher resolution and a narrower field of view 288. Thedescribed arrangement of the imaging devices is an example. Otherconfigurations are within the scopes of various embodiments. In otherexamples, a single imaging device maybe sufficient for image capturingdescribed herein, provided that the imaging device has a sufficientlywide field of view and/or a sufficiently high resolution. In otherexamples, an imaging device having an adjustable field of view and/or anadjustable resolution is used.

At least one of the first imaging device 201 or second imaging device202 is movable relative to the substrate support, and therefore, movablerelative to the substrate 208 supported on that substrate support. Forexample, the first imaging device 201 is mounted at a distal end of anarm 262 which has its proximal end attached to a pivot 264. The pivot264 is mounted on and slidable along a rail 266 supported by one of thestands 120, i.e., stand 120A. The arm 262 may be telescopicallyextendible or retractable to adjust its length as shown by arrow 272.The arm 262 is further rotatable about the pivot 264 as shown by arrow274, and the proximal end of the arm 262 is movable along the rail 266as shown by arrow 276. Likewise, the second imaging device 202 ismounted at a distal end of an arm 282 which has its proximal endattached to a pivot 284. The pivot 284 is mounted on and slidable alonga rail 286 supported by the other of the stands 120, i.e., stand 120B.The arm 282 may be telescopically extendible or retractable to adjustits length. The described arrangement for moving the first imagingdevice 201 and/or the second imaging device 202 is an example. Otherconfigurations are within the scopes of various embodiments.

The movement of the first imaging device 201 and/or second imagingdevice 202 relative to the substrate 208 is controlled by the controller118 via precise positioning devices, such as servo motors. As a results,actual positions of the first imaging device 201 and/or second imagingdevice 202 in the frame of reference of the printing system 200 areknown to the controller 118, and may be used by the controller 118 todetermine actual positions of one or more marks recognized from imagescaptured by the first imaging device 201 and/or second imaging device202.

In an example, the first imaging device 201 with its larger field ofview 268 may be used first to capture a wide-area, intermediate image ofthe substrate 208 so as to increase the likelihood that a mark 290 onthe substrate 208 may be included in the intermediate image. Based onthe captured wide-area image, the controller 118 recognizes the mark290, using a known algorithm as described herein. The actual position ofthe recognized mark 290 is determined based on at least the actualposition of the first imaging device 201 at the time the wide-area imagewas captured. However, due to the lower resolution of the first imagingdevice 201, the actual position of the recognized mark 290 determinedbased the wide-area image of such a lower resolution may not besufficiently accurate in some situations. In such cases, the secondimaging device 202 with the higher resolution is moved under control ofthe controller 118 to the position of the mark 290 determined from thewide-area image to capture another, high-resolution image, which permitsthe actual position of the mark 290 in the frame of reference of theprinting system to be determined at higher accuracy. The actual positionof the mark 290 is then used for determining the actual positions of oneor more print regions on the substrate 208, as described herein. Thehigh accuracy at which the actual position of the mark 290 is determinedcontributes to high print precision.

In a further example, the second imaging device 202 may be moved undercontrol of the controller 118 so that an expected position of the mark290 may fall within the field of view 288 of the second imaging device202. The expected position (or preset position) of the mark 290 isknown, e.g., from design data supplied to the printing system 200 for aprint job to print on the substrate 208. In an example, the design dataincludes the ideal or expected positions, in the frame of reference ofthe printing system, of features consistent with the ideal or expectedposition information used for the fabrication of the previous layers(e.g., a black matrix) on the substrate. The ideal or expected positionsmay be obtained from a CAD (Computer-Aided Design) drawing used for thefabrication of the substrate.

If the mark 290 is indeed present within the narrower field of view 288of the second imaging device 202, the mark 290 may be recognized from ahigh-resolution image captured by the second imaging device 202 and theactual position of the mark 290 may be determined at high accuracy,without capturing another image, based on at least the actual positionof the second imaging device 202 at the time the high-resolution imagewas captured. However, if, due to substrate fabrication or markinstallation errors, the mark 290 was not present within the narrowerfield of view 288 of the second imaging device 202 and, as a result wasnot recognized from the high-resolution image captured by the secondimaging device 202, the first imaging device 201 with its wider field ofview 268 will be moved in to capture an intermediate wide-area image foridentifying the mark 290 before the second imaging device 202 is usedagain for precise determination of the actual position of the mark 290,as described above.

The above described sequence of using two imaging devices to capturemultiple images of marks is an example. In other examples, a singleimaging device with an adjustable field of view and/or an adjustableresolution, e.g., with zooming capability, may be used instead ofmultiple imaging devices, for capturing both wide-area andhigh-resolution images. In another example, a single image that both hasa high resolution and covers a wide area of the substrate may besufficient for high-precision mark acquisition, without requiringmultiple images, as described with respect to FIGS. 3A-3B below.

FIG. 3A is a schematic side view of a printing system 300 in accordancewith one embodiment. FIG. 3B is a schematic top view of a substrate 308in the printing system 300 of FIG. 3A in an example. In one embodiment,the printing system 300 includes one or more features of the printingsystem 100 and the printing system 200 described herein. Compared to theprinting system 200 where one or more imaging devices each having anarray of image sensors arranged in multiple columns and rows, theprinting system 300 includes at least one line scan imager having imagesensors arranged in a line. A printing system can use both an imagingdevice with an array of image sensors as described with respect to FIG.2 and a line scan imager with a line of image sensors as described withrespect to FIGS. 3A-3B.

As shown in FIG. 3A, the printing system 300 comprises the substratesupport 102, the printhead assembly 119, and a line scan imager 303. Theprinthead assembly 119 is movably coupled to the print support 116, andis positioned facing the substrate support 102. The line scan imager 303is coupled to the print support 116 or the printhead assembly 119, andis also positioned facing the substrate support 102. The line scanimager 303 is movable along the print support 116.

The printhead assembly 119 comprises dispensing nozzles 206 extendingtowards the substrate support 102. The printhead assembly 119 and theline scan imager 303 are positioned facing the substrate support 102 inan ejection direction 325 in which print material is to be ejected fromthe dispensing nozzles 206 of the printhead assembly 119 onto asubstrate 308 supported on the substrate support 102. Here, theprinthead assembly 119 is coupled with the rail 117 by an air bearingassembly or other low friction coupling means (not shown), and a linearactuator including, for example, a motor or other driver and coupledbetween the printhead assembly 119 and one or both of the stands 120A,120B moves the printhead assembly 119 in the cross-scan direction. Theline scan imager 303 is coupled to the print carriage 322 that carriesthe printhead assembly 119, and is therefore moveable together with theprinthead assembly 119 along the rail 117 of the print support 116relative to the substrate support 102. The line scan imager 303 iscoupled to a rail 313 supported by the print carriage 322 to be movedalong the rail 313 by, for example, a motor or a servomotor. As aresult, movement of the line scan imager 303 along the print support 116can be controlled, for example, by the controller 118, to be effected bymovement of the printhead assembly 119 along the print support 116, orby movement of the line scan imager 303 along the rail 313 relative tothe printhead assembly 119, or both. In another example, the line scanimager 303 is fixed to the print carriage 322 and is movable along theprint support 116 by movement of the print carriage 322 and theprinthead assembly 119. In another example, the line scan imager 303 iscoupled to the print support 116 to be movable independently of theprinthead assembly 119. In another example, more than one line scanimager like the line scan imager 303 is included in the printing system300 to capture multiple images during a single pass of the substrate 308in the Y direction under the line scan imagers.

The line scan imager 303 is configured to capture at least one imageincluding at least one mark on the substrate 308. The line scan imager303 converts the image to data or signals that are transmitted to thecontroller 118, or another controller (e.g. the system controller 129 ofFIG. 1) of the printing system 300. The controller 118 receives thesignals, which are converted to image data, or the image data from theline scan imager 303. From the image data, the controller 118 determinesthe actual position of the at least one mark, as described with respectto FIG. 2. The actual position of the mark is then used for determiningthe actual positions of one or more print regions on the substrate 308,as described herein. This print region determination is a process thatenables controlling the printing system 300 to print with highprecision. Another optional process that helps involves nozzle mapping.For nozzle mapping, the printing system 300 includes an imaging device302 oriented in the Z direction opposite to the ejection direction 325for capturing at least one image including a plurality of marks on abottom surface (or nozzle surface) 329 of the printhead assembly 119.The captured image is transferred to the controller 118, or anothercontroller of the printing system 300, which is coupled to the imagingdevice 302 as shown in FIG. 3A. The marks on the nozzle surface 329 theprinthead assembly 119 are recognized, e.g., by the controller 118, fromthe image transferred from the imaging device 302 for mapping positionsof the dispensing nozzles 206 to the frame of reference of the printingsystem 300. The mapped positions (or actual positions) of the one ormore print regions of the substrate 308 and the mapped positions of thedispensing nozzles 206 in the same frame of reference are used forcontrolling ejection of the print material from the dispensing nozzles206 onto the one or more print region of the substrate 308. Because themapped positions of the dispensing nozzles 206 and the one or more printregions reflect the actual positions of the dispensing nozzles 206 andthe one or more print regions with high accuracy, printing accuracy isimproved. In an example configuration, the imaging device 302 for nozzlemapping is a line scan imager which captures an image including thenozzle surface 329 of the printhead assembly 119 while the printheadassembly 119 passes by the imaging device 302 in the scan direction (Xdirection). In at least one embodiment, the imaging device 302 isomitted.

FIG. 3B is a schematic plan view of the substrate 308 in the printingsystem 300 of FIG. 3A in an example. More specifically, FIG. 3B shows acombined view of a top plan view of the substrate 308 (as seen downwardin the ejection direction 325 in FIG. 3A) placed side-by-side with abottom plan view of a bottom surface of the line scan imager 303 (asseen upward in the Z direction in FIG. 3A) for comparison.

The line scan imager 303 comprises a plurality of image sensors 332. Inthe example configuration in FIG. 3B, all image sensors 332 of the linescan imager 303 are arranged in a single line, e.g., line 331, along thecross-scan direction (X direction). In another embodiment (not shown),the image sensors 332 of the line scan imager 303 are arranged in morethan one lines. For example, the image sensors 332 in a first line areconfigured as primary image sensors for capturing image data, whereasimage sensors 332 in a second line can be configured as redundancy orsecondary sensors for providing image data in case one or more primaryimage sensors fail, or additional sensors for improving signal-to-noiseratio of the image data. The image sensors 332 are photoelectric devicesthat capture light reflected from the substrate 308 toward the line scanimager 303 and register electric signals in accordance with the capturedlight. The image sensors 332 capture an image including one or moremarks on the substrate 308 as described herein, while the substrate 308is moving under and relative to the line scan imager 303 in the scandirection (Y direction). In this aspect, the image capturing by the linescan imager 303 is similar to that performed by a copying machine or ascanner which uses a similar linear photo sensor arrangement. To captureimages including marks or features having dimensions in the range of afew μm, for example, 5-10 μm, the image sensors 332 are configured toprovide a high resolution of, for example, about 0.1 μm. Examples ofimage sensors include, but are not limited to, CMOS (complementary metaloxide semiconductor) and CCD (charge coupled device) sensors.

To capture an image using the line scan imager 303, the line scan imager303 is controlled by the controller 118 to move in the X direction to aposition where a mark to be captured may fall within the field of viewof the line scan imager 303. The line scan imager 303 is thentemporarily fixed in the X direction with respect to the substratesupport, and the substrate 308 is moved by the substrate support in theY direction for image capturing for capturing the mark. For example,during such movement of the substrate 308 in the Y direction, the linescan imager 303 passes over an area of the substrate 308 between lines373, 374. The width of this area, or the distance between lines 373,374, corresponds to a length of the line 331 of the image sensors 332 inthe X direction. The controller 118 controls the line scan imager 303 tocapture images of regions 383, 384, 385 (hereinafter referred to asimages 383, 384, 385) between the lines 373, 374. The image 383 iscaptured at a location where a mark 520 is expected to be found.Similarly, the image 384 is captured at a location where marks 522 and560 are expected to be found, and the image 385 is captured at alocation where a mark 562 is expected to be found. The expectedpositions of the marks on the substrate 308 are included in design datasupplied to the printing system for printing on the substrate 308. Thedesign data include at least printing data of the design to be printedon the substrate 308 as coordinates in the frame of reference of theprinting system. Based on the design data and prior to image capturing,the controller 118 controls movement of the line scan imager 303 in theX direction such that the expected positions of the marks to be imagedfall within the field of view of the line scan imager 303, e.g., theexpected positions of the marks 520, 542, 560, 562 fall within the areabetween the lines 373, 374. In at least one embodiment, some of theimages 383, 384, 385 are combined in a single image. For example, bothmarks 520, 522 may be included in a single image extending along the Ydirection, and both marks 560, 562 may be included in another singleimage extending along the Y direction. The image(s) captured by the linescan imager 303 in the printing system 300 is/are used in a mannersimilar to the images captured by the first imaging device 201 and/orthe second imaging device 202 of the printing system 200. However, theline scan imager 303 can capture high-resolution images that cover awide area, depending on the size or length of the line 331 of imagesensors 332 in the X direction and/or the length of the capturedimage/area in the Y direction. As a result, multiple image capturing inan example as described with respect to the first imaging device 201and/or second imaging device 202 may be avoidable when the line scanimager 303 is used.

A description will be now given for the substrate 308 in FIG. 3B whichwill serve as an example substrate to be mapped to the frame ofreference of the printing system in accordance with some embodiments,using one or more imaging devices as described with respect to theprinting system 200 and/or one or more line scan imagers as describedwith respect to the printing system 300. In an example, the substrate308 is a glass substrate, but other materials such as plastics orceramics may be used in the various printers described herein.

The substrate 308 comprises at least one substrate alignment feature,and a plurality of print region alignment features. An alignment featuremay be any feature that has one or more known properties, that indicatesat least one of a position or an orientation of an object, and that canbe captured in image data and can be recognized from the captured imagedata. A substrate alignment feature indicates at least one of a positionor an orientation of a substrate. A print region alignment featureindicates at least one of a position or an orientation of at least oneprint region on the substrate. For example, alignment features may bemarks, sometimes referred to as “fiducial marks,” with one or more knownproperties such as patterns, orientations, dimensions, and positions onthe substrate 308. The marks are attached to (e.g., by adhesive), oretched or machined in, or printed or painted on the substrate 308. Othermanners for providing marks to a substrate may be used. Any numberand/or shape and/or material and/or orientation of the marks may beused. Any of the marks may include text, bar code, company's name and/orlogo. With a higher number of marks and/or more complex mark shapes, theaccuracy of the positions of the print regions determined using themarks increases. Alignment features may also include features inherentto or included in the substrate 308. In an example, one or more edgesand/or one or more corners of the substrate 308 may serve as alignmentfeatures. In a further example, a feature included on the substrate 308from a previous process may serve as an alignment feature. Examples ofsuch features include pixel wells or sub-pixel wells in a black matrixmaterial, or other pixel or area definition, in which print material isto be deposited. Solely for the sake of simplicity, marks are used asalignment features in the following description of example embodiments.

In the example configuration in FIG. 3B, the substrate 308 includes, assubstrate alignment features, one or more substrate marks 501, 511, 521,531 arranged at corresponding one or more corners of the substrate 308.Each of the substrate marks 501, 511, 521, 531 is in a shape of a crosswith a position and an orientation known from the design data. Thesubstrate marks 501, 511, 521, 531 together precisely indicate thepositions of the substrate 308 in the frame of reference of the printingsystem. The shape and/or size and/or number and/or orientation and/orrelative position within the substrate, of the substrate marks 501, 511,521, 531 are examples only. Other configurations are within the scopesof various embodiments. For an example, a single substrate mark, such assubstrate mark 501, may be sufficient to indicate positions of thesubstrate 308, provided that the substrate mark 501 has a known spatialrelationship with the corresponding corner 301 of the substrate 308. Ina further example, an edge or corner of the substrate 308 may be used asa substrate mark. While one substrate mark may be sufficient in somesituations, the accuracy of material deposition can increase when morethan one substrate marks are provided on the substrate 308.

Besides the substrate marks, the substrate 308 further includes aplurality of print region marks for recognizing and mapping a pluralityof print regions to the frame of reference of the printing system. Forthe sake of simplicity, print region marks are referred to in thefollowing description simply as “marks.” In the example configuration inFIG. 3B, the substrate 308 includes seven print regions sp1-sp7, eachcorresponding, for example, to a display panel to be manufactured. Toidentify positions of the print regions, the substrate 308 includes foreach print region one or more marks. Specifically, each of the printregions sp1-sp5 are identified by a set or group of fours marks at itscorners, whereas the print regions sp6 and sp7 share a common set offour marks 590, 592, 594, 596, at corners of the area where the printregions sp6 and sp7 are located. In FIG. 3B, for the sake of simplicity,reference numerals are omitted for some of the marks. Marks 510, 512,514, 516 are provided on the substrate 308 for identifying the printregion sp1, marks 520, 522, 524, 526 are provided on the substrate 308for identifying the print region sp3, and marks 560, 562, 564, 566 areprovided on the substrate 308 for identifying the print region sp4.

In some other approaches, a limited set of marks are provided fordefining an entire substrate, without a separate set of marks forindividual print regions. For example, some approaches may include onlythe substrate marks 501, 511, 521, 531 on the substrate 308, and thenuse the substrate marks 501, 511, 521, 531 to calculate positions of theprint regions, based on substrate layout design information, with theassumption that the print regions are perfectly arranged as intended onthe substrate. Such approaches may fail to account for and remedysituations where, due to, e.g., substrate fabrication errors, the printregions may not be arranged as intended. For example, as shown in FIG.3B, the print region sp1 has placement error compared to the other printregions. Placement error can include X-Y offset, rotation, scaling,skew, and keystoning (imaging perpendicularity) error. The inaccuraciesin the calculated positions of the print regions, especially those printregions with placement errors, affect the printing accuracy in the otherapproaches.

FIG. 4 is a flowchart of a printing method 400 in accordance with oneembodiment. FIGS. 5A-5D are schematic plan views of the substrate 308 ora portion of the substrate 308 being processed at various operations ofthe printing method in FIG. 4. The printing method 400 may be performedin any of the printing systems 100, 200 and 300 by, or under control of,at least one controller as described herein. In the description below,the printing method 400 is performed by, or under control of, thecontroller 118.

At operation 405, at least one image of a substrate supported in aprinting system is acquired. For example, the controller 118 acquires atleast one image of the substrate 308 supported in the printing system200 or 300 from the first imaging device 201 and/or second imagingdevice 202 of the printing system 200, or the line scan imager 303 ofthe printing system 300, respectively. The at least one image iscaptured at an expected position of a target mark. In the followingdescription, the line scan imager 303 is used for image capturing.

FIG. 5A is a schematic plan view of a portion of the substrate 308 wherethe substrate mark 501 may be located in accordance with the designdata. An image 506 of this portion of the substrate 308 is captured andtransferred to the controller 118, as signals or image data, for markrecognition. According to the design data for the substrate 308, thesubstrate mark 501, in its expected form shown in dotted lines in FIG.5A, has the shape of a cross. The cross is formed by a vertical element502 and a horizontal element 503 which intersect each other at a centerpoint 504, and which are oriented in the Y direction and X direction,respectively. The X-Y coordinates of the center point 504 in the frameof reference of the printing system are known from the design data as anexpected position 504A of the substrate mark 501. The dotted line figurein FIG. 5A is shown for explanation purposes, and is not captured in theimage 506. The image 506 is captured by moving the line scan imager 303under control of the controller 118 to a location where the substratemark 501 at its expected position may fall within the field of view ofthe line scan imager 303, and then the image 506 is captured. Datarepresenting the captured image 506 is acquired or generated by thecontroller 118 from the transmissions of the line scan imager 303.

At operation 415, an actual position of a first alignment feature on thesubstrate is determined based on the at least one captured image. Forexample, referring to FIG. 5A, the controller 118 determines the actualposition of the substrate mark 501 based on data representing the image506. For this purpose, the controller 118 performs a mark recognitionprocessing to recognize the substrate mark 501 from the image data,using the known properties of the substrate mark 501 included in thedesign data stored in and/or accessible by the controller 118. Imageprocessing algorithms and/or software and/or programs for recognizingobjects based on their known properties such as patterns, positions,sizes and/or orientations are known in the art of image processing, andare not described in detail herein.

When the substrate mark 501 is not recognizable from the captured image506, the controller 118 controls image recapturing by the line scanimager 303. In an example, the image recapturing involves repositioningthe line scan imager 303 to a new location along the X direction tobetter correspond to the expected position 504A of the substrate mark501. In a further example, the image recapturing involves adjusting theresolution and/or field of view of the line scan imager 303 to image awider area of the substrate 308. When an imaging device such as a camerais used for image capturing, image recapturing is performed as describedwith respect to FIG. 2. The controller 118 then performs again a markrecognition processing to recognize the substrate mark 501 from therecaptured image.

In at least one embodiment, it may not be necessary to capture the wholemark. Rather, when a portion of a mark is sufficient for determinationof the mark position, capturing an image including such portion issufficient to define an entire substrate. As such, “one or more imagesincluding one or more marks,” or similar wordings, used herein does notrequire the whole mark to be capture in the image(s); instead, capturinga portion that permits recognition of the mark from an image of thecaptured portion for subsequent determination of the mark position issufficient.

Recognizing a mark means that a controller has determined that an image,either a single image or a composite image, contains a mark. When a markis recognized by the controller, processing is triggered to map the markto the frame of reference of the printing system, by determining theactual position of the mark in the printing system frame of reference.As a result of mark recognition and mapping processing, with or withoutimage recapturing, the recognized substrate mark 501, shown in solidlines in FIG. 5A, is found at an actual position 504B in the frame ofreference of the printing system. The controller 118 can determine theactual position of the recognized substrate mark 501 based on the knownactual positions of the capturing line scan imager 303. The actualposition 504B has X-Y coordinates shifted from those of the expectedposition 504A. The orientation of the recognized substrate mark 501 mayalso be different from its expected orientation, as shown by angle abetween the vertical element 502 of the recognized substrate mark 501 atthe actual position 504B and the Y direction. In an example, thedescribed image capturing and mark recognition processing are performedto acquire more than one substrate marks, such as substrate marks 501,511, 521, 531 on the substrate 308. In a further example, the actualpositions of one or more other substrate marks 511, 521, 531 arecalculated based on the determined actual positions of the substratemark 501, and the design data that includes known relationships amongthe substrate marks. The determined actual positions and/or orientationsand/or other actual properties of the one or more substrate marks areused by the controller 118 to determine actual positions and/ororientation of the substrate 308, based on known relationships in thedesign data between the one or more substrate marks and the substrate308. The determined actual positions and/or orientation of the substrate308 may be used by the controller 118 to physically adjust the substrate308 and/or to make correction to printing data of the design to beprinted on the substrate 308.

At operation 425, expected positions of a plurality of second alignmentfeatures on the substrate are determined, based on the actual positionof the first alignment feature. For example, the controller 118 uses theactual positions and/or orientations of one or more of the substratemarks 501, 511, 521, 531 determined at operation 415 to calculateexpected positions of the print region marks, based on knownrelationships in the design data between the one or more substrate marksand the print region marks. An example technique for calculating theexpected positions of the print region marks is bilinear interpolationincluding one or more interpolation operations such as translational,rotational, skew and scaling.

FIG. 5B is a schematic plan view showing the substrate 308 asascertained by the controller 118 as a result of the operation 425. InFIG. 5B, the actual positions of the substrate marks 501, 511, 521, 531are determined at operation 415, and are shown at their actual positionsin solid lines. The print region marks are not yet recognized or mapped,and are shown at their respective expected positions in dotted lines. Itshould be noted that, in this example, the marks 510, 512, 514, 516corresponding to the misplaced print region sp1 described with respectto FIG. 3B are still expected to be at positions close to ideal orexpected positions defined in the design data.

At operation 435, actual positions of the second alignment features aredetermined based on the at least one image and the expected positions ofthe second alignment features. For example, the controller 118 performsa mark recognition processing in an area of the image captured at theoperation 405 where the expected position determined at the operation425 indicates that a print region mark may be located. This is possiblein situations where the image captured at the operation 405, e.g., bythe line scan imager 303, is a high-resolution image that covers a largearea of the substrate 308 where one or more substrate marks and one ormore print region marks are located. Thus, one or more print regionmarks are already included in the captured image, and may be processedfrom the same image without image recapturing. In situations where thecaptured images do not cover all print region marks, additional imagesare captured in a manner similar to the operation 405.

The actual positions of the recognized print region marks are determinedfrom the captured image data in a manner similar to the operation 415.All print region marks indicating a print region may be recognized andtheir actual positions may be determined from the captured image(s). Forexample, all print region marks 520, 522, 524, 526 indicating the printregion sp3 may be recognized and their actual positions may bedetermined from the captured image(s). This arrangement provides printregion definition at high accuracy. However, in some situation, theactual position of at least one print region mark indicating a printregion may be calculated from the actual positions of the other printregion marks indicating the same print region. For example, some printregion marks 510, 512, 514 indicating the print region sp1 arerecognized and their actual positions are determined from the capturedimage(s); however, the actual position of the remaining print regionmark 516 indicating the same print region sp1 is calculated from thedetermined actual positions of the other print region marks 510, 512,514. This arrangement sacrifices some accuracy in print regiondefinition for a faster processing speed. Such accuracy sacrifice mayaffect printing precision, and eventually the printed product quality,when the print region sp1 is significantly misplaced as described withrespect to FIG. 3B.

FIG. 5C is a schematic plan view showing the substrate 308 asascertained by the controller 118 as a result of the operation 435. InFIG. 5C, all substrate marks and print region marks have been mappedinto the printing system frame of reference from the operations 415 and435, and are shown at their actual positions in solid lines. The printregions indicated by the print region marks are not yet acquired and areshown in dotted lines. That is, the coordinates of every print locationwithin the respective print regions, in the frame of reference of theprinting system, have not yet been determined. The controller 118 hasnow determined, and may have quantified and/or flagged, that the printregion sp1 is not at its expected position (FIG. 5B) but is actuallymisplaced (FIG. 5C). This detected placement error of the print regionsp1 permits the controller 118 to make corrections to improve printingaccuracy, as described herein. In at least one embodiment, not all printregion marks are processed at once. For example, the print region markscorresponding to the print region sp1 and print region sp2 are processedfirst so that printing can proceed in the print region sp1 and printregion sp2. While a printing operation is being performed in the printregion sp1 and print region sp2, the print region marks corresponding tothe print regions to be printed next, i.e., the print region sp3 andprint region sp4 are mapped, and so on. This arrangement reduces theprocessing and printing time for the whole substrate 308 by performingoperations in parallel.

At operation 445, target positions of a plurality of print regions onthe substrate are determined based on the actual positions of the secondalignment features. As used herein, “target position” of a print regionor pixel is the actual position of the print region or pixel in theframe of reference of the printing system, and is the location where aprinthead assembly of the printing system is controlled to deposit printmaterial. The design data may include a coordinate map representingexpected positions of the marks and at least corners of thecorresponding print regions, for example, as X-Y coordinates in theframe of reference of the printing system or the substrate. Taking theprint region sp3 as an example, once the marks 520, 522, 524, 526, havebeen mapped by the controller 118, the actual positions of the marks520, 522, 524, 526 are compared to their positions known/expected fromthe design data. From the comparison, the controller 118 derives arelationship for converting between the positions of the marks 520, 522,524, 526, as determined from the captured image(s) and theirknown/expected positions from the design data. The derived relationshipand the expected positions of corresponding corners 540, 542, 544, 546of the print region sp3 in the design data are used by the controller118 to determine actual positions of corners 540, 542, 544, 546 of theprint region sp3 in the frame of reference of the printing system.

The controller 118 then determines actual positions of all pixels to beprinted in the print region sp3 from the actual positions of the corners540, 542, 544, 546. An example technique for determining the actualpositions of the pixels from the corners is bilinear interpolationincluding one or more interpolation operations such as translational,rotational, skew and scaling. Alternatively, in a thin filmencapsulation (TFE) application where a thin film is to be depositedover the print region sp3 instead of individual pixel printing, thecontroller 118 determines actual positions of the boundary of the printregion sp3 from the actual positions of the corners 540, 542, 544, 546.The determination of actual positions of marks, print region corners,pixels or boundaries in the frame of reference of the printing system isalso referred to herein as mapping. In some embodiments, nozzle mappingis performed by the controller 118 in a similar manner to determineactual positions of the dispensing nozzles of the printhead assembly119, based on nozzle surface marks (not shown) included in the nozzlesurface 329 and one or more images including such nozzle surface markscaptured by the imaging device 302.

FIG. 5D is a schematic plan view showing the substrate 308 asascertained by the controller 118 as a result of the operation 445. InFIG. 5D, all substrate marks, print region marks and print regions arealready mapped from the operations 415, 435, 445 and are shown at theiractual positions or target positions in solid lines. This is an exampleonly. As noted above, one or more print regions may be processed while aprinting operation is being performed in one or more other printregions.

Although in the above description, print region recognition and mappinginvolves capturing and processing marks for each print regionindividually, the present disclosure is not so limited. For example,print region definition may involve capturing and processing a set ofmarks 590, 592, 594, 596 common for several print regions, for example,as shown in FIG. 5D for the print region sp6 and print region sp7. Whenall common marks 590, 592, 594, 596 have been captured and recognized,actual positions of the pixels or boundaries of the print region sp6 andprint region sp7 are determined, e.g., by interpolation, from the actualpositions of the common marks 590, 592, 594, 596, and also based on thedesign data which specifies expected positions or relationships of theprint region sp6 and print region sp7 with respect to the marks 590,592, 594, 596.

At operation 455, ejection of print material onto the substrate in theplurality of print regions is controlled based on the determined targetpositions of the print regions. For example, based on the actualpositions of the pixels or boundaries of the print region sp3 and/or theactual positions of the dispensing nozzles of the printhead assembly 119in the frame of reference of the printing system, the controller 118controls ejection of print material from the dispensing nozzles of theprinthead assembly 119 to the print region sp3 of the substrate 308. Inone embodiment, this print material ejection control includes physicaladjustments of the substrate 308 and/or the printhead assembly 119,and/or logical modification of print data to be used for generation ofcontrol signals for the dispensing nozzles to eject print material.Because the determined actual positions of the dispensing nozzles and/orthe print region sp3 reflect the real physical positions of thedispensing nozzles and the print region sp3 with high accuracy, printingaccuracy is improved.

Specifically, the actual positions of the dispensing nozzles and theprint regions are in the same frame of reference of the printing system,and are used by the controller 118 to control, when and/or whichdispensing nozzles to eject print material in accordance with the designdata which include(s) printing data or coordinates in the frame ofreference of the substrate. For example, if a print nozzle is found at alocation different from its expected location by a distance d, a dropletejected according to an existing print plan will arrive at a locationdifferent from its target location t by the distance d. If the distanced has an x-component (distance in the X direction) d_(x), the printheadassembly can be adjusted by −d_(x) to compensate. If the print nozzlesdeviate in the X direction from their expected locations by an averagedistance d _(x) the print assembly can be adjusted by −d _(x) tocompensate. If the distance d has a y-component d_(y), the print plancan be adjusted with a global firing delay of d_(y)/ν, where ν is thetranslation velocity of the substrate in the Y direction, and likewisefor a y-component of the average distance d _(y). As a result, printedproducts with high printing precision are obtainable.

In one embodiment, printed products manufactured by the describedprinting method include, but are not limited to, solar panels, and flatpanel displays such as organic light emitting diode (OLED) displays.

FIG. 6A is a flowchart of a printing method 600 in accordance with oneembodiment. FIG. 6B is a schematic plan view of the print region sp3 onthe substrate 308 being processed in the printing method 600 in FIG. 6A.The pixel sizes in FIG. 6B are exaggerated for illustrative purposes.The printing method 600 may be performed in any of the printing systems100, 200 and 300 by, or under control of, at least one controller asdescribed herein. In the description below, the printing method 600 isperformed by, or under control of, the controller 118. In oneembodiment, the printing method 600 includes one or more features of theprinting method 400 described herein.

At operation 605, at least one image including alignment features on asubstrate is acquired. For example, the controller 118 acquires at leastone image including one or more marks from the first imaging device 201and/or second imaging device 202 of the printing system 200, or the linescan imager 303 of the printing system 300, in a manner similar tooperation 405 of the printing method 400.

At operation 615, actual positions of the plurality of alignmentfeatures in a frame of reference of the printing system are determinedbased on the at least one image. For example, the controller 118determines, from the captured image, the actual positions of the marks520, 522, 524, 526 indicating the print region sp3, in a manner similarto the operation 415 and/or the operation 435 of the printing method400.

At operation 625, target positions of pixels at corners of a printregion on the substrate are determined based on the actual positions ofthe alignment features. For example, the controller 118 compares theactual positions of the marks 520, 522, 524, 526 to their presetpositions in the design data to derive a relationship or transformfunction for converting between the actual positions of the marks 520,522, 524, 526, e.g., as determined from the captured image(s), and theirpreset positions from the design data. The derived transform functionand preset positions of the corners 540, 542, 544, 546 in the designdata are used by the controller 118 to determine actual positions of thecorners 540, 542, 544, 546.

At operation 635, target positions of pixels along edges of the printregion are determined based on the target positions of the pixels at thecorners of the print region. For example as shown in FIG. 6B, thecontroller 118 uses the actual positions of the corners 540, 546 todetermine a first edge 620 of the print region sp3, the actual positionsof the corners 540, 542 to determine a second edge 630, the actualpositions of the corners 542, 544 to determine a third edge 640, and theactual positions of the corners 544, 546 to determine a fourth edge 650of the print region sp3.

For a TFE application, the controller 118 may now proceed to operation655 to control the printhead assembly to deposit a thin film over theprint region sp3 within a boundary defined by the determined edges 620,630, 640, 650 of the print region sp3.

For printing at individual pixels in the print region sp3, thecontroller 118 determines actual positions of pixels 622, 624 along thedetermined first edge 620 based on a number of pixels per row of theprint region sp3 in the X direction from the design data, e.g., bydistributing the pixels evenly along the first edge 620. Similarly, thecontroller 118 determines actual positions of pixels 642, 644 along thedetermined third edge 640 based on the same number of pixels per row.

At operation 645, target positions of pixels in the print region aredetermined based on the target positions of the pixels along the edgesof the print region. For example as shown in FIG. 6B, the controller 118determines actual positions of pixels 631, 671 along the determinedsecond edge 630 based on a number of pixels per column of the printregion sp3 in the Y direction from the design data. Similarly, thecontroller 118 determines actual positions of pixels 636, 676 along thedetermined fourth edge 650 based on the same number of pixels percolumn. For pixels inside the print region sp3, the controller 118 firstdetermines a column 660 of pixels based on corresponding determinedpixels 622, 642 on the corresponding first and third edges 620, 640. Thecontroller 118 then determines actual positions of pixels 632, 672 alongthe determined column 660 based on the number of pixels per column.Similarly, the controller 118 determines a column 670 of pixels based oncorresponding determined pixels 624, 644 on the corresponding first andthird edges 620, 640, and then determines actual positions of pixels634, 674 along the determined column 670 based on the number of pixelsper column. The described processing is repeated until the actualpositions of all pixels in the print region sp3 have been determined.

In at least one embodiment, the operations 625, 635, 645 of the printingmethod 600 are performed in the operation 445 of the printing method 400for determining target positions of print regions on a substrate basedon actual positions of print region marks.

At operation 655, ejection of print material from dispensing nozzles ofa printhead assembly onto the print region of the substrate iscontrolled based on the target positions of the pixels in the printregion. For example, the controller 118 controls ejection of printmaterial in a manner similar to operation 455 of the printing method400.

FIG. 7 is a flowchart of a printing method 700 in accordance with oneembodiment. The printing method 700 may be performed in any of theprinting systems 100, 200 and 300 by, or under control of, at least onecontroller as described herein. In the description below, the printingmethod 700 is performed by, or under control of, the controller 118. Inone embodiment, the printing method 700 includes one or more features ofthe printing methods 400, 600 described herein.

At operation 705, at least one imaging device is controlled to capturefirst images of a plurality of first alignment features on a substrate.For example, the controller 118 controls the first imaging device 201and/or second imaging device 202 to capture one or more first imagesincluding substrate marks 501, 511, 521, 531 on the substrate 308, in amanner similar to operation 405 of the printing method 400.

At operation 715, actual positions of the first alignment features inthe frame of reference of the printing system are determined based onthe first images. For example, the controller 118 performs a markrecognition process on the captured first images to recognize thesubstrate marks 501, 511, 521, 531 from the captured first images, andthen determines actual positions of the recognized substrate marks, in amanner similar to operation 415 of the printing method 400. In somesituations, multiple image capturing by multiple imaging devices areperformed, as described with respect to FIG. 2.

At operation 725, expected positions of a plurality of second alignmentfeatures are determined based on the actual positions of the pluralityof first alignment features. For example, the controller 118 determinesexpected positions of the print region marks based on the actualpositions of the substrate marks, in a manner similar to operation 425of the printing method 400.

At operation 727, a relative position of the at least one imaging deviceand a substrate support supporting the substrate is controlled based onthe expected positions of the second alignment features to enableimaging of the second alignment features using the at least one imagingdevice. For example, the controller 118 performs control to re-positionthe first imaging device 201 and/or second imaging device 202 so thatone or more expected positions determined at operation 725 for one ormore print region marks may fall within the field of view of the firstimaging device 201 and/or second imaging device 202.

At operation 729, the at least one imaging device is controlled tocapture second images of the second alignment features. For example,after the re-positioning at operation 727, the controller 118 controlsthe first imaging device 201 and/or second imaging device 202 to captureone or more second images including the expected positions of one ormore print region marks.

At operation 735, actual positions of the second alignment features inthe frame of reference of the printing system are determined based onthe second images. For example, the controller 118 performs a markrecognition processing on the second images captured at the operation729 to recognize one or more print region marks from the captured secondimages, and to determine actual positions of the recognized print regionmarks, in a manner similar to operation 715. In some situations,multiple image capturing by multiple imaging devices are performed, asdescribed with respect to FIG. 2.

In situations where the fields of view of the first imaging device 201and/or second imaging device 202 are not sufficiently wide to captureone or more print region marks and/or substrate marks in a first image,the at least one imaging device can be repositioned, as in operation727, and subsequent images captured, as in operation 729. Where an imagecaptured by a line scan imager, such as the line scan imager 303 of FIG.4, may cover a sufficiently wide area of the substrate 308 to capturetarget marks, a separate image capturing process can be avoided.

At operation 745, target positions of print regions corresponding togroups of the second alignment features are determined based on theactual positions of the second alignment features. For example, thecontroller 118 determines target positions of a print region based onthe actual positions of the corresponding set of print region marks, ina manner similar to operation 445 and/or operations 625, 635, 645.

At operation 755, ejection of print material from dispensing nozzles ofa printhead assembly onto the substrate in the print regions iscontrolled based on the target positions of the print regions. Forexample, the controller 118 controls print material ejection in a mannersimilar to operation 455.

In some cases, the line scan imager can be used to correct the positionof a substrate on the substrate support 102 (FIG. 1). Thus, instead of,or in addition to, performing operation 755 above, a repositioningoperation can be performed to improve the positioning of the substrateon the substrate support. In one example, the actual positions of thesubstrate marks can be compared to expected positions of the substratemarks based on design data for the substrate and a deviation parametercan be determined by any of the controllers or processors describedherein. The deviation parameter may be determined in a number of ways.In one example, a deviation of each substrate mark from its designposition can be determined, and the deviation parameter can be set tothe maximum of the deviations. In another example, the deviationparameter can be set to the average of the deviations. In anotherexample, the deviation parameter can be set to the deviation of apredetermined substrate mark.

The deviation parameter is then compared to a tolerance to determinewhether the substrate needs to be repositioned. Any of the controllersor processors described herein can perform the comparison. If thesubstrate needs to be repositioned, the printing system is controlled toperform the standard substrate positioning routine over again. Thisprocess can be repeated until the deviation parameter is withintolerance, at which time operation 755 above can be performed.

The described methods include example operations, but they are notnecessarily required to be performed in the order shown. Operations maybe added, replaced, changed order, and/or eliminated as appropriate, inaccordance with the spirit and scope of embodiments of the disclosure.Embodiments that combine different features and/or different embodimentsare within the scope of the disclosure and will be apparent to those ofordinary skill in the art after reviewing this disclosure.

FIG. 8 is a block diagram of a controller, in accordance with oneembodiment. One or more of the units and/or systems and/or operationsdescribed with respect to FIGS. 1-7 is/are realized in one embodiment byone or more controllers 800 of FIG. 8.

The controller 800 comprises a hardware processor 802, a storage device804 including at least one non-transitory, computer readable storagemedium, a bus 808, an I/O (input/output) interface 810, and a networkinterface 812. The processor 802 is coupled with the storage device 804,the I/O interface 810, and the network interface 812 via the bus 808.The network interface 812 is connectable to a network 814, so that theprocessor 802 and the storage device 804 are communicable with otherdevices via the network 814. The processor 802 is configured to executecomputer program instructions encoded in the storage device 804 and/orto access data stored in the storage device 804 to cause the controller800 to perform one or more functionalities and/or operations describedwith respect to FIGS. 1-7.

The processor 802 includes one or more of a central processing unit(CPU), a multi-processor, a distributed processing system, anapplication specific integrated circuit (ASIC), and/or a suitablehardware processing unit.

The storage device 804 includes one or more of an electronic, magnetic,optical, electromagnetic, infrared, and/or a semiconductor system (orapparatus or device) for storing instructions and/or data in anon-transitory manner. For example, the storage device 804 includes asemiconductor or solid-state memory, a magnetic tape, a removablecomputer diskette, a random access memory (RAM), a read-only memory(ROM), a rigid magnetic disk, and/or an optical disk. As examples ofoptical disks, storage device 804 includes a compact disk-read onlymemory (CD-ROM), a compact disk-read/write (CD-R/W), and/or a digitalvideo disc (DVD).

The I/O interface 810 is circuitry that is connectable with externalcircuitry. For example, the I/O interface 810 includes one or more of akeyboard, keypad, mouse, trackball, trackpad, cursor direction keys,card reader, communication port, display, signal light, printer and/oraudio device for communicating information to/from the processor 802. Inan example, the I/O interface 810 is omitted.

The network interface 812 is circuitry that allows the controller 800 tocommunicate with the network 814, to which one or more other controllersand/or image capturing/processing equipment are connected. For example,the network interface 812 includes one or more of wireless networkinterfaces such as BLUETOOTH, WIFI, WIMAX, GPRS, or WCDMA; or wirednetwork interface such as ETHERNET, USB, or IEEE-1394. In an example,the network interface 812 is omitted.

By being configured to execute some or all of functionalities and/oroperations described with respect to FIGS. 1-7, the controller 800enables the realization of one or more advantages and/or effectsdescribed with respect to FIGS. 1-7.

Alignment features on a substrate can be located quickly if thesubstrate has a layout that is generally known in advance such that theprinting system can be configured to take advantage of the substratelayout. If a series of substrates having similar, or the same, layoutare to be processed, a printing system can be configured with cameraslocated and actuated to focus on the likely positions of alignmentfeatures to locate the alignment features quickly on successivesubstrates.

In one case, a substrate has six panels defined across the width of thesubstrate. The panels can define single display devices to be formed onthe substrate or groupings of display devices to be formed on thesubstrate. Configuring a printing system with cameras to acquire andlocate alignment marks quickly for such substrates is summarized in thesupplemental figures attached to this application in an Appendix. Here,the substrate has one or more first alignment features, sometimes calledfiducial marks, and each panel on the substrate is defined using one ormore second alignment features. Because it is generally known in advancethat the substrate has six panels of substantially equal size and shapeuniformly spaced across the width of the substrate, cameras or lineimagers can be positioned along a print support, as described herein,and actuated to locate the first and second alignment features.

In this case, a first camera system comprising one or more camerascaptures a wide image of one or more areas of the substrate. Thesubstrate is scanned from an input side of the printing system to anoutput side of the printing system for a first scan, and the firstcamera system captures a first image, or a plurality of first images, ofthe substrate during the first scan. The first scan captures images ofat least two of the first alignment features, and may also capture oneor more of the second alignment features. The first scan may capture animage of the entire substrate, or the first scan may only capture thoseareas of the substrate where first alignment features are expected to befound. Thus, a single first image may include more than one firstalignment feature captured in multiple images and logically combined, orthe first scan may capture a plurality of first images.

The substrate is typically positioned at the input end of the printingsystem for processing. The substrate is placed against positioningfeatures, such as physical posts or banks, which initialize the positionof the substrate. The substrate positioning system acquires a secureattachment to the substrate for further positioning. The substratetypically has opposite first and second ends and opposite first andsecond sides. The first end of the substrate passes under the variousimaging systems followed by the second end. As noted above, the firstimage or plurality first images includes at least two of the firstalignment features, and may include more than two. If the two firstalignment features are located at the first end of the substrate, thenthe first scan may be just a partial scan of the substrate, just toimage the first alignment features expected to be found near the firstend.

In one case, the first alignment features may be expected to reside nearthe corners of the substrate, so wide area cameras can be located onboth sides of the substrate processing surface of the printing system tocapture wide area images of the substrate near those expected locations.Each wide area camera has a field of view large enough to mootconceivable error in locating the first alignment features so the widearea cameras are virtually certain to capture the first image (orimages). In one embodiment, error in positioning the first alignmentfeatures is about 2 mm, and wide area cameras having a viewing field of10-13 mm are used.

The first image or images is/are analyzed using image processingsoftware to identify alignment features therein. The image processingsoftware searches for first alignment features by a localized searchinformed by an expected location of the first alignment features. Theexpected location is defined as coordinates in a first coordinate systemdefined for the printing system, as described elsewhere herein, and isbased on a pre-defined layout of the substrate that includes coordinatesof alignment features in a second coordinate system defined for thesubstrate. A mathematical transformation relating the second coordinatesystem to the first coordinate system is based at least in part on ahome location of the substrate when the substrate is loaded into theinput side of the printing system. Thus, the expected locations of allalignment features, including the first and second alignment features,is known by transforming the coordinates of the alignment features fromthe pre-defined layout to the first coordinate system using themathematical transformation.

The image processing software determines, at least, an alignment of thefirst alignment features, by determining an x coordinate and a ycoordinate of each first alignment feature. As described herein, the ydirection is the scan direction of the substrate and the x direction isthe direction within the plane of the substrate perpendicular to the ydirection. If the first alignment features should have the same xcoordinate value, the extent to which the x coordinates of the firstalignment features are not the same indicates a rotational error of thesubstrate. As noted elsewhere herein, the substrate positioning systemis operable to rotate the substrate incrementally to align the xcoordinates of the first alignment features based on the alignment errordetermined from processing the image or images of the substrate. Arotation angle can be defined in radians as the x coordinate differenceof the first alignment features divided by the y coordinate differenceof the first alignment features. To the extent the aligned x coordinatesof the first alignment features deviate from an expected location of thesubstrate based on a pre-defined substrate processing plan, thepositioning system can also position the substrate to correct globalx-error of the substrate. Alternately, for purposes of capturing imagesof alignment features, camera positions can be adjusted for the globalx-error of the substrate.

The positioning system may also be configured to position the substrate,or a portion thereof, in the z direction, which is the directionsubstantially perpendicular to the substrate processing surface of theprinting system (and to the x and y directions). The positioning systemmay have a precision z actuation component, for example a z-axis linearactuator coupled to the substrate engagement portion of the positioningsystem, to perform z positioning of the portion of the substrate engagedby the positioning system. In many cases, the substrate is engaged withthe positioning system at an edge of the substrate, so the z actuationcomponent positions the edge of the substrate in the z direction. Thiscan have the effect of positioning the entire substrate at leastsomewhat in the z direction and/or positioning the edge of the substratein the z direction. In many cases, the substrate is floating on a gascushion that precisely defines a gap between the substrate and thesubstrate processing surface independent from movement by thepositioning system. Working together, the gas cushion and thepositioning system can precisely position the substrate a distance abovethe substrate processing surface that is pre-defined in the substrateprocessing plan, and can render the substrate flat to a high degree ofprecision across the extent of the substrate, including the edge portionwhere the positioning system engages with the substrate.

The image processing and alignment actions described above may beperformed while the substrate is positioned at the output side of theprinting system following the first scan. In the event the substrate isnot scanned entirely to the output side of the printing system duringthe first scan, the substrate may wait in a partially scanned positionwhile image processing and alignment are performed, or the substrate maybe moved back to the input side of the printing system for alignment.Having aligned the substrate and positioned the substrate according tothe substrate processing plan, a second scan is performed wherein thepositioning system moves the substrate from the output side to the inputside of the printing system, or vice versa. During the second scan, asecond camera system comprising one or more cameras captures a pluralityof second images of the substrate. Each camera of the second camerasystem is positioned based on an expected location of one or more secondalignment features, the expected location based on the pre-definedsubstrate layout corrected according to the alignment performedfollowing the first scan.

The second camera system has high magnification cameras to capture highresolution images of the second alignment features. In one instance, thehigh magnification cameras have a view field that is about 1 mm in size,so each high magnification camera can capture one alignment feature insize less than about 1mm, and may be able to capture more than onealignment feature in one scan if the alignment features are close than 1mm separation distance. Typically, as the substrate is scanned, thecameras of the second camera system will activate when an alignmentfeature to be imaged is expected to arrive within the view field of oneof the cameras of the second camera system, and will deactivate when thealignment feature is expected to pass out of the view field. Theexpected time of arrival of alignment features within the field of viewof a camera is determined using the pre-defined layout of the substrate,corrected for any positioning of the substrate done during calibration.

The second scan may result in images being captured of all secondalignment features. In some cases, however, one scan may not result inimages being captured of all the second alignment features. For example,if some second alignment features are too close to be imaged by onecamera at the scan speed of the second scan, due to camera cycle time,one or more alignment features may be missed during the second scan, anda third scan may be needed to capture those that were missed. In suchcases, an alternative is to slow down the scan speed so that allfeatures can be imaged in one scan. Another alternative is to use morethan one camera to image alignment features in one column.

Each second image is processed by the image processing software todetermine actual locations of at least two second alignment features foreach panel defined on the substrate. Because the substrate layout isgenerally known in advance, a camera of the second camera system isdeployed to capture an image for each panel defined on the substrate.Each camera of the second camera system thus captures an image of atleast two alignment features for each panel defined on the substrate.The cameras of the second camera system are high magnification cameraswith limited field of view, but because the substrate is aligned, andthe expected locations of the second alignment features from thepre-defined layout are used to position the cameras of the second camerasystem, each second image contains a high resolution image of at leastone second alignment feature. The precisely determined actual locationsof the second alignment features are used to adjust the print plan forany error in positioning the panels on the substrate.

In the case where six panels are defined across the width of thesubstrate, six high magnification cameras can be included in the secondcamera system and positioned at locations where second alignmentfeatures are expected to be found on the substrate. Each camera of thesecond camera system captures one or more images of the substrate as thesubstrate is scanned during the second scan. Multiple images can belogically joined by image processing software, if desired, or the imagesmay be taken only in the vicinity of expected locations of alignmentfeatures such that there are gaps between the locations of the images.In any event, the six high magnification cameras capture images of atleast two second alignment features of each panel defined on thesubstrate. Capturing images of more than two second alignment featuresof each panel can increase certainty of panel positioning and systemcalibration.

It should be noted that a single camera configuration of a printingsystem may be used to align and calibrate the printing system forsubstrates having different layouts and sizes. In general, if theprinting system has n high magnification cameras, a substrate with mpanels can be aligned and calibrated to the printing system if m is lessthan n. Because the range of travel of the high magnification cameras isknown and positioning of the cameras can be based on the known range oftravel, a camera can be positioned at the expected x location ofalignment features if there are as many cameras as panels. The same istrue for substrates having sections with different panel layouts. Forexample, a substrate may have a first section with three panels definedin the first section, and a second section with six panels defined inthe second section. A portion of the six high magnification cameras inthe second camera system, in this case three cameras, can be used toimage the second alignment features for the three panels of the firstsection, and all the cameras can be used to image the second alignmentfeatures for the panels of the second section. If the second section hasfewer panels than the total number of cameras in the second camerasystem, a second portion of the cameras of the second camera system canbe used to image second alignment features for the panels of the secondsection.

The first camera system and the second camera system are each coupled tothe print support substantially as described elsewhere herein. Eachcamera has a carriage that couples to a rail of the print support. Tworails can be defined on the print support, one for each camera system.Alternately, both camera systems may be supported on only one rail. Inthe two-rail case, the cameras of the first camera system can be coupledto, and actuated along, the first rail while the cameras of the secondcamera system are coupled to, and actuated along, the second rail. Thus,each camera of the first camera system has a range of motion limited byneighboring cameras, but since the cameras of the first camera systemare wide view cameras, the first image can be captured by positioningthe cameras of the first camera system at locations where firstalignment features are expected to be found. Likewise for the cameras ofthe second camera system. The cameras of the second camera system canalso be repositioned during the second scan if sections of the substratehave different panel layouts that require camera repositioning duringthe second scan. In some cases, the cameras of the second camera systemmay be moved slightly during scanning to capture images of secondalignment features with close-by x coordinates.

FIG. 9 is a schematic isometric view of a print assembly 900 accordingto one embodiment. The print assembly 900 features a plurality ofcameras deployed in a first camera system 902 and a second camera system904. The print assembly 900 can be used to practice the embodimentsdescribed above that use a first camera system and a second camerasystem. The first camera system 902 comprises a plurality of firstcameras 906, and the second camera system 904 comprises a plurality ofsecond cameras 908. The first and second cameras 906 and 908 may be thesame kind of camera, or may be different kinds of cameras. In oneembodiment, the first cameras 906 are wide view cameras and the secondcameras 908 are high-resolution cameras.

The print assembly 900 has a print support 910, which is like the rail117 of FIG. 1. The print support 910 supports the first and secondcameras 906 and 908 to traverse over and across a substrate 912 disposedon a substrate support 914 under the print support 910. Not shown here,the dispenser assembly 114 can be coupled to the print support 910, asin FIG. 1. Note that the print support 910, substrate 912, and substratesupport 914 are shown truncated for size.

The first and second cameras 906 and 908 are coupled to, and supportedby, the print support 910 in a spaced-apart relationship to thesubstrate support 914 to provide clearance between devices supported bythe print support 910 and the substrate 912. The cameras 906 and 908 areeach coupled to a camera support 916. The camera supports 916 coupled tothe first cameras 906 are all coupled to a first track of the printsupport 910, which is not visible here but may be a groove in anunderside surface of the print support 910 that faces the substratesupport 914. The camera support 916 coupled to the second cameras 906are coupled to a second track of the print support 910 in a similar way.The camera support 916 are configured to move past each other on the twotracks without colliding, thus enabling the first and second cameras 906and 908 to be positioned along the print support 910 withoutinterference between any of the first cameras 906 and any of the secondcameras 908. This enables the first cameras 906 to be moved andpositioned at any desired locations with respect to the substrate 912while also positioning the second cameras 908 at any desired locationindependent of the first cameras 906. Each camera support 916 typicallyhas actuators, for example driven wheels or air bearings, that engagewith a groove or shelf formed on or in the lower surface of the printsupport 910 to provide positioning capability. The cameras 906 and 908are coupled to the camera supports 916 in an orientation to allow thefield of view for each camera 906 and 908 to encompass a portion of thesubstrate 912. It should be noted that some of the cameras 906 and 908may be fixed to the print support 910 and unmovable with respect to theprint support 910, but at least some of the cameras 906 and 908 aremovable with respect to the print support 910. For example, the outercameras of each camera group can be fixed, while cameras between theouter cameras may be actuated.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

1. A printing method, comprising: acquiring images of a substratesupported in a printing system, wherein said images comprise: a firstimage captured by a first imaging device having a first resolution, anda second image captured by a second imaging device having a secondresolution higher than the first resolution; determining an actualposition of a first alignment feature on the substrate in a frame ofreference of the printing system based on the first image; determiningan actual position of a second alignment feature in the frame ofreference of the printing system based on the second image; determininga target position of a print region on the substrate based on the actualposition of the second alignment feature; and controlling ejection ofprint material onto the substrate in the print region based on thetarget position of the print region, wherein capturing the second imageis based on the actual position of the first alignment feature.
 2. Theprinting method of claim 1, wherein the first image includes the firstalignment feature, the second image includes the second alignmentfeature, and the second image is captured by positioning the secondimaging device based on the actual position of the first alignmentfeature.
 3. The printing method of claim 2, wherein the first imagingdevice includes a wide view camera that captures the first image duringa first scan of the substrate from a first side of the printing systemto a second side of the printing system, and the second imaging deviceincludes at least one high magnification camera that captures the secondimage during a second scan of the substrate from the second side of theprinting system to the first side of the printing system.
 4. Theprinting method of claim 3, further comprising aligning the substratebetween the first scan and the second scan.
 5. The printing method ofclaim 4, wherein the aligning the substrate comprises aligning thesubstrate in two orthogonal directions.
 6. The printing method of claim1, further comprising determining a placement error of the substrate,wherein determining the target position of the print region comprisescompensating for the placement error.
 7. The printing method of claim 2,further comprising: before said capturing the first image by the firstimaging device, moving the first imaging device along a print support toa position corresponding to an expected position of the first alignmentfeature on the substrate; and before said capturing the second image,moving the second imaging device along the print support to a positioncorresponding to an expected position of the second alignment feature onthe substrate, wherein said controlling ejection of the print materialcomprises moving a printhead assembly along the print support whileejecting the print material from dispensing nozzles of the printheadassembly onto the print region of the substrate.
 8. A printing method,comprising: capturing a first image of a substrate supported in aprinting system; determining an actual position of a first alignmentfeature on the substrate in a frame of reference of the printing system,based on the first image; capturing a second image of the substratebased on the actual position of the first alignment feature, wherein thesecond image is captured at higher magnification than the first image;determining an actual position of a second alignment feature in theframe of reference of the printing system based on the second image;determining a target position of a print region on the substrate basedon the actual position of the second alignment feature; and controllingejection of print material onto the substrate in the print region basedon the target position of the print region.
 9. The printing method ofclaim 8, wherein the first image is captured by a wide view cameraduring a first scan of the substrate from a first side of the printingsystem to a second side of the printing system, and the second image iscaptured by a high magnification camera during a second scan of thesubstrate from the second side of the printing system to the first sideof the printing system.
 10. The printing method of claim 9, wherein thefirst side is an input side of the printing system, and the second sideis an output side of the printing system.
 11. The printing method ofclaim 8, further comprising aligning the substrate between the firstscan and the second scan.
 12. The printing method of claim 11, whereinthe aligning the substrate comprises aligning the substrate in twoorthogonal directions.
 13. The printing method of claim 12, furthercomprising determining a placement error of the print region.
 14. Theprinting method of claim 13, wherein the placement error is an alignmenterror or a rotation error.
 15. The printing method of claim 14, furthercomprising determining an actual position of an edge of the printregion.
 16. The printing method of claim 15, further comprising:determining an expected position of the second alignment feature basedon the actual position of the first alignment feature; and determining arelationship between the expected position and the actual position ofthe second alignment feature.
 17. A printing method, comprising:capturing a first image of a substrate supported in a printing system,using a camera configured to have a first resolution or a first field ofview; determining an actual position of a first alignment feature on thesubstrate in a frame of reference of the printing system based on thefirst image; adjusting the camera to have a second resolution higherthan the first resolution or a second field of view narrower than thefirst field of view; capturing a second image of the substrate, usingthe camera adjusted to have the second resolution or the second field ofview; determining an actual position of a second alignment feature inthe frame of reference of the printing system based on the second image;determining a target position of a print region on the substrate basedon the actual position of the second alignment feature; and controllingejection of print material onto the substrate in the print region basedon the target position of the print region.
 18. The printing method ofclaim 17, wherein the first image and the second image are capturedduring a plurality of scans of the substrate.
 19. The printing method ofclaim 18, further comprising aligning the substrate along two orthogonaldirections at least once during the plurality of scans.
 20. The printingmethod of claim 18, further comprising moving the camera to a targetposition before starting the plurality of scans.